The invention relates to a method for eliminating foam in a drum-type washing machine and to a drum-type washing machine that is suitable for performing said method. The invention relates in particular to a method for eliminating foam that is present in a detergent solution tub of a drum-type washing machine having a program controller for controlling a program sequence comprising a sequence of steps which include an adding of water and a rotating of the drum, as well as to a drum-type washing machine that is suitable therefor.
In conventional drum-type washing machines, spinning is performed at high revolutions already after the main wash and the rinse cycles. If there is a lot of foam present or if a lot of foam is produced during spinning, the detergent solution drain pump will not convey the foam/detergent solution mixture. Thus, if foam is detected during the pump's drain-off operation, spinning will not be performed, or in the case of foam being detected during a spinning cycle, spinning will be aborted. Moreover, the foam can escape from the apertures in the detergent solution tub as well as from the detergent solution tub ventilation and the filler hose. Early foam detection and efficient measures for eliminating the foam are therefore important.
According to DE 41 04 151 A1, the foam is destroyed by switching on a heater. In order to destroy the foam in the wider environment of the heater also, the drum is rotated slowly so that further foam reaches the heater and is destroyed there by the introduction of heat.
DE 43 34 969 A1 discloses a device for destroying detergent foam which has an apparatus for generating hot air which is introduced through a supply line in the detergent solution tub wall between the detergent solution tub and the drum.
Methods for removing foam in a detergent solution tub of a drum-type washing machine are also known from DE 102 34 472 A1 and DE 198 46 248 A1.
DE 102 34 472 A1 describes a method for eliminating foam in a detergent solution tub of an electronically controlled drum-type washing machine following a program step that is provided for draining water from the detergent solution tub, comprising a detergent solution discharge system disposed at the base of the detergent solution tub, having a detergent solution drain pump and having a sensor for determining the level of the liquid contained in the detergent solution tub. The waveform of the sensor signal (P) that is recorded during the operation of the detergent solution drain pump includes a gradient Δp/Δtn compared to Δpn-1/Δtn-1 which indicates the presence of foam, whereupon a foam treatment measure adapted to the gradient is then initiated.
In EP 0 278 239 A1, excessive foam formation in the main wash cycle which can be observed during the heating of detergent solution in the detergent solution tub is eliminated by addition of a limited amount of cold water and/or by temporarily switching off the detergent solution heater.
In addition, usually in special method sequences, the foam is removed by suitable rinse baths while avoiding as far as possible the input of mechanical energy (by long drum idle times, for example).
A disadvantage with the known methods is that they sometimes lead to a considerable lengthening of the overall wash program, greatly increased water consumption and poor results during spinning.